Liquid developer for use in electrophotographic transfer process

ABSTRACT

A liquid developer for use in the electrophotographic transfer process comprising a liquid carrier with an electric resistance of not less than 109 Omega .cm and a dielectric constant not greater than 3, having dispersed therein a toner comprising particles of a colored substance coated with at least one resinous substance which will penetrate cloth or paper, together with fine particles being harder than the toner particles and having an average particle diameter of from 1 to 15 Mu .

United States Patent Machida Oct. 28, 1975 LIQUID DEVELOPER FOR USE IN3,512,965 5/1970 M'atkan 252 621 L ELECTRQPHQTQGRAPHIC TRANSFER3,766,072 10/1973 Metcalfe et aL. 117/37 LE 3,806,339 4/1974 Tamai117/37 LE PROCESS Inventor: Hazime Machida, Tokyo, Japan KabushikiKaisha Ricoh, Tokyo, Japan Filed: July 27, 1973 Appl. No.: 383,259

Assignee:

Foreign Application Priority Data July 27, 1972 Japan 47-74604References Cited UNITED STATES PATENTS 12/1960 Wright 252/621 L PrimaryExaminerMaynard R. Wilbur Assistant Examiner-N. Moskowitz Attorney,Agent, or Firm-Coo'pe'r, Dunham, Clark, Griffin & Moran 57 ABSTRACT Aliquid developer for use in the electrophotographic transfer processcomprising a liquid carrier with an electric resistance of not less than10 Q.cm and a dielectric constant not greater than 3, having dispersedtherein a toner comprising particles of a colored substance coated withat least one resinous substance which will penetrate cloth or paper,together with fine particles being harder than the toner particles andhaving an average particle diameter of from 1 to 15 1,.

5 Claims, No Drawings LIQUID DEVELOPER FOR USE IN ELECTROPHOTOGRAPI-IICTRANSFER PROCESS BACKGROUND OF THE INVENTION This invention is concernedwith liquid developers for use in electrophotography. It is moreparticularly concerned with such developers for use in the transferprocess for reproducing an image.

The principal methods for developing electrostatic latent images formedon an electrophotographic copying material are the dry developing methodemploying a powdery toner and the wet developing method employing aliquid toner.

Based on the differences in obtained the final copy, the methods arealso classified as direct and indirect, or transfer. In the directprocess, the final image is formed directly on the electrophotograhicmaterial. In the transfer process, the image is formed on theelectrophotographic material and transferred to another support, such asplain paper.

Theoretically, both dry and wet developing can be used in both thedirect and the transfer methods.

One advantage of wet developing is that the edging effect whichincreases the resolving power of the finished product is minimizedcompared with the dry developing procedure. The major advantage of thetransfer procedure is that the final product is on plain paper. Becauseof these advantages, it has long been a desideratum of the art tocombine the transfer process with wet developing.

The art has not yet developed a satisfactory procedure which combinesthe transfer process with wet developing. The reason for this is that animage formed by dry developing can be readily transferred to a papersheet by the application of bias voltage, but a wet developed imageadheres tenaciously to the photoconductive layer of theelectrophotographic material and is difficult to transfer.

THE INVENTION A liquid developer has now been discovered in accordancewith this invention which makes it possible to combine wet developingwith the transfer process, without any loss of image quality. Thedeveloper of this invention comprises a carrier liquid having anelectrical resistance of at least l Q'cm and a dielectric constant up to3, having dispersed therein a toner comprising particles of a coloredsubstance coated with at least one resin which is capable of penetratinginto paper or cloth together with fine particles being harder than thetoner particles and having an average diameter of from 1 to l5;1..

The average particle diameter of the fine particles is obtained bydispersing them in an appropriate liquid, placing a measured amount ofthe suspension on a thin glass plate, and forming a sandwich by placinganother glass plate over the suspension. The thin layer of thesuspension is photographed with a photomicroscope and the diameter of200 to 1,000 particles within a visual field is measured. The averageparticle diameter represents the mode size, i.e., the particle diameterwhich has been detected most frequently.

The colored particles employed in the preparation of the toners used inthis invention include any of those pigments or dyes normally employedin the preparation of liquid developers. The particles are coated with asoft resin of the type normally employed in the preparation of printinginks. Such inks form images on paper because they readily penetrate thepaper, thus forming an image which is strongly bonded thereto. Thepenetration also contributes to increasing the drying rates of the inks.Attempts to utilize these resins in previous methods of preparing tonersfor liquid development have not been successful. The reasons for thisare (l) at the time of transfer the toner particles, since they arecoated with a soft resin, are crushed resulting in a blurred image, and(2) the image is also blurred as a result of the toners diffusingthrough the capillaries of the paper. More precisely, such toners havepoor resolving power.

Any of a wide variety of pigments or dyestuffs may be used as thecolored materials for the toners of this invention. The following may bementioned by way of example of typical materials presently commerciallyavailable: Carbon Black MITSUBISHI No. 44, Carbon Black MITSUBISHI No.(both of these are the manufacture of MITSUBISHI KASEI K.K.), Printex G,Special Black 15 (a manufacture of Deggusa Co.), Mogal A, Sutetex,Peerless 155 (all of these are the manufacture of Columbia Co.), Elftex5 (a manufacture of Cabot Co. Acetylene Black (a manufacture of DENKIKAGAKU K.K.), Cyanine Black, Spirit Black (both of these are themanufacture of ORIENT KASEI K.K.), Aniline Black (a manufacture ofI.O.l. Co., England), Brilliant Carmine 68 (a manufacture of SANYOSHIKISO K.K. Rhodamine B (a manufacture of TOYO INK K.K. BenzidineYellow GNH (a manufacture of SANYO SHIKISO K.K., Ultra Rose E (amanufacture of TOYO INK K.K.), Cyanine SANYO SHIKISO K.K.,Phthalocyanine Green E7G (a manufacture of DAINICHI SEIKA K.K.),CyanineBlue LBG (a manufacture of SUMITOMO KAGAKU K.K. Benzidine Yellow GR (amanufacture of TOYO INK K.K. Oil Blue, Alkali Blue (both of these arethe manufacture of ORIENT KASEI K.K.), Ultra Blue B (a manufacture ofTOYO INK K.K.), Spilon Yellow, Spilon Red (both of these are themanufacture of HODO- GAYA KAGAKU K.K.), Microlith Black C-T, MicrolithBlue 4CT, Microlith Green CT, Microlith Yellow 2CT, Microlith Red R-T(all of these are the manufacture of CHIBA, Ltd.), Reflex Blue AG, etc.As particles having a composition similar to these colored particles,there are Graphofax Toner Powder No. 39-50, a dry toner (a manufactureof Hunt Co.), etc., and these are also applicable to the presentinvention. 1

A variety of resinous substances may be purchased 0 prepared for use inthe invention. They may be coated on the foregoing colored particlesthrough kneading, for instance. They include, for example butyl rubberssuch as ESSO Butyl 215 and E880 Butyl by ESSO Oil Co., isobutyl rubberssuch as Vistanex LM and Vistanex MN by ESSO Oil Co., chlorinatedisobutylene rubbers such as Butyl Rubber HT -l066, Butyl Rubber HT-l067and Butyl Rubber HT-l068 by ESSO Oil Co., alkyd resins such as BeckozolI343, Beckozol J-l334, Beckozol J-534, Beckozol P-789, Beckorin P-75,Beckozol P-450, Beckozol J-6l l, Beckozol J-7l9 and Beckasite J-8l l byDAINIPPON INK K.K., isobutylene butylene copolymers such as Vistaron4608 and Vistaron 4504 by ESSO Oil Co., and styrene butadiene copolymerssuch as Pliolite S-5A, Pliolite 8-63 and Plioflex 1502 by GoodyearCorp., under the trade names of JSR-0060, SBR 1500 and SBR 1502 byNIPPON GOSEI GOMU K.K., under the trade names of Solprene 1205, Solprene1204, Solprene 235 and Solprene. 303 by Fillips Co., and under the tradename of Nipol 1220 and Hycar 1432 by NIPPON-ZEON Co.

In addition to the above enumerated resinous substances, varnish,linseed oil, rosin, modified rosin, tung oil, soybean oil, fish oil,various waxes, various celluloses, asphalt, aliphatic amine resins, etc.may also be used. Typical examples of this type of resinous substancesinclude KO-Blown Asphalt, TOKUKO-Blown Asphalt, S. P-Blown Asphalt (allof these are the manufacture of NIPPON SEKIYU K.K.), Varnish 30, Varnish50, Alkyd-modified Varnish (all of these are the manufacture ofDAINlPPON INK K.K.), Linseed Oil (a manufacture of WAKO JUNYAKU K.K.),etc.

Mixtures of the above resins may be employed as well as mixtures ofthese highly penetrative resinous substances with other well knownresins conventionally employed in wet developers for electrostaticphotography, such as acrylic resins, styrene resins, polyester resins,etc., in the proportion of 0.5 4 parts by weight of the latter resin per1 part by weight of the former resin. The quantity of penetrative resincoated on the particles of the colored substances is substantially thesame as in conventional toners employed in the wetdeveloping method.Typically, the toners will include 1 30 parts by weight of resin to 1part by weight of the particles of said colored substance.

The term a resinous substance being capable of penetrating into a paperor a cloth as used herein refers to materials responding to thefollowing test:

A resinous substance is dissolved in a mixed solvent, the mixing ratioof toluene and petroleum aliphatic hydrocarbon being 1:1, to prepare a40 wt.% resinous solution. A 0.5 mm thick metal plate having a hole mmin diameter is placed on an Indian paper and the hole is filled with thesolution. Any excess resinous solution on the surface of the metal plateis removed with a spatula so that the quantity of filled resinoussolution is just equal to the volume of the hole. The metal plate isremoved gently so that the resinous solution alone remains on the paper.It is allowed to stand under atmospheric pressure at C. for 10 minutesand the diameter of a circle of the impregnated resinous solution ismeasured. If the circle is more than 20 mm in diameter, the resin is ofsufficient permeability to be used in the invention. If it is less than20 mm in diameter, the resin is not suitable for use in the invention.

The above described toners are suspended in the carrier liquid togetherwith additional fine particles which are, generally speaking, harderthan the toners so that they are not themselves crushed during transfer,and they help to prevent crushing of the toners. Typical examples ofsuch toners include inorganic materials such as glass beads, zinc oxide,titanium dioxide, silica and the like. Many of the toner particlespresently employed in the dry developing method can also be used as thefine particles of this invention.

The weight ratio of toner to fine particles in the liquid developers ofthis invention is from 0. 1:1 to 1:1. Some variation from this range canbe tolerated. It has been observed, however, that appreciably below thisrange there is not a satisfactory improvement in the formability of theimage or its distinctness, while above the range there is an undesirableincrease in the number of white spots in the body of the image.

The average particle diameter of the fine particles is from 1 to 1511..Only a relatively small amount of variation from this range can betolerated. Below the range, there is a loss of image clarity; above it,there is an increase in the number of white spots.

While there is no intention to be limited by theory, it appears that inthe liquid developers of this invention, the toner particles suspendedin the carrier liquid are adsorbed to the fine particlesv The fineparticles therefore play, so to speak, the role of carriers for thetoner particles. Therefore, unless the fine particles have a diameter asdescribed above, they will not remain dispersed in the carrier liquidand a distinct image cannot be formed at the time of development ortransfer. The ability to faithfully transfer the toner from the surfaceof the photoconductive layer of a copying material to the surface of atransfer material is enhanced by the ability of the fine particles toprevent crushing of the toner and its diffusion through capillaries ofthe paper fibers.

The carrier liquid may be any of the conventional liquids utilized inordinary liquid developers. They are generally characterized aspetroleum aliphatic hydrocarbons with an electric resistance of at least10 Qcm and a dielectric constant up to 3. Among the presently availablecommercial carriers which may be employed in the invention, there maybe, for example: Shell S.B.P., Shellzol (all of these are themanufacture of Shell Oil Co.), lsopar E, lsopar G, lsopar H, lsopar K,lsopar L} lsopar M, Naphtha No. l, Naphtha No. 2, Naphtha No. 3, NaphthaNo. 5, Naphtha No. 6, S01- v'esso 100, Solvesso 150 (all of these arethe manufacture of Esso Chemical Co.), Pegazol 1030, Pegazol 2130,Pegazol 2l30-C, Pegazol 3040, Pegazol AS- 100, Pegazol ARO-40 (all ofthese are the manufacture of Mobil Oil Co.), etc., is applicable.

The following non-limiting examples are given by way of illustrationonly:

Butyl rubber 20 g 50% toluene solution of styrene butadiene copolymer(molar ratio 30 z lsopar G mixture of the above composition wassubjected to 24" hours kneading for dispersion in a ball-mill, whereby aconcentrated toner containing a highly penetrative resin was prepared.Subsequently, by dispersing 25 g of this concentrated toner and 15 g ofzinc oxide (having average particle diameter of 1.];1.) in 500 ml oflsopar G, a liquid developer having a satisfactory transferability foruse in wet-type electrostatic photography was prepared.

An electrostatic latent image was formed on a selemium photoconductiveplate through electrification and exposure by the known method, and wasthen developed with the foregoing liquid developer. Next, by superposingan ordinary paper on the image formed by developing as above, the imagewas transferred to the paper. The transferred image was distinct and notblurred.

EXAMPLE 2 In the same way as in Example 1 except for replacing the fineparticles of zinc oxide with titanium oxide having the same particlediameter as the zinc oxide, a liquid developer for use in wet-typeelectrostatic'photography was prepared.

When an electrostatic latent image was developed with this liquiddeveloper and transferred to paper, there was obtained a satisfactorytransferred .copied image equal in quality to that inExample 1.

EXAMPLE 3 In the same way as in Example 1 except for replacing the fineparticles of zinc oxide with silica (having average particle diameter of2p), a liquid developer for use in wet-type electrostatic photographywas prepared.

When an electrostatic latent image was developed with this liquiddeveloper and transferred to paper, there was obtained a satisfactorytransferred copied image equal in quality to that in Example 1.

EXAMPLE 4 EXAMPLE 5 Ultra Blue B g Special Black 50 g lsoprene 30 g 50%toluene solution of methyl methacrylate styrene copolymer (molar ratio50 50) 60 g A mixture having the above composition was subjected to 24hours kneading for dispersion in a ballmill, whereby a concentratedtoner containing a highly penetrative resin was prepared. Subsequently,by dispersing 25 g of this concentrated toner and 0.8 g of glass beads(having average particle diameter of 5p.) in 50 ml of Isopar H, a liquiddeveloper having a satisfactory transferability for use in wet-typeelectrostatic photography was prepared.

Next, an electrostatic latent image formed in the same way as in Example1 was developed with the foregoing liquid developer, and this image wastransferred to an ordinary paper superposed thereon. As a result,substantially all of the toner on the photoconductive plate wastransferred to the paper, and the transferred image was distinct.

EXAMPLE 6 Through the same procedure as in Example 5 except forreplacing isoprene with butyl rubber (Butyl Rubber HT-lO-68), a liquiddeveloper for use in electrostatic photography was prepared.

When development and transfer were performed in the same way as inExample 1 utilizing this liquid developer, the transferred image on anordinary paper was as good as that in Example 5, and the tonertransferability was also satisfactory.

v g I Comparative Tests In order to confirm the superiority of thetransferability of liquid developers of the present invention, thefollowing comparative tests were conducted in which two types of controldevelopers were prepared and their resolving power at the timeof'transferwas compared with that of the liquid developers of thepresentinvention.

Preparation of Control Developer Test Procedure A seleniumphotoconductive plate was first charged with electricity by coronadischarge. Then, upon superposing thereon a chart for measuringresolving power with one to several tens of lines drawn within fixedlengths, it was exposed and then developed with control developer-A.Subsequently, an ordinary paper was superposed on the image-carryingsurface and was thereafter stripped off, to transfer the image from theselenium photoconductive plate to the paper. Then, the resolving powerin lines per mm was determined.

The same tests as above were also conducted with control developer-B andthe liquid developers of the present present invention prepared inExample 3 and Example 5. The results were as shown in the followingTable 1.

Table l Resolving Power Liquid Developer (lines/mm) Liquid developer ofExample 1 12 Liquid developer of Example 5 13 Control developer-A 5Control developer-8* The copied image on the paper had numerouswhite'spots, so that calculation of exact number of lines wasimpossible.

The same tests as above were also conducted with liquid developersprepared in Examples 1, 2, 4 and 6.

What is claimed is:

l. A liquid developer for use in electrophotographic transfer processwhich comprises: a carrier liquid having an electric resistance of atleast lO fl'cm and a dielectric constant up to 3; a toner dispersed insaid carrier liquid, said toner comprising particles of a coloredsubstance and at least one resinous substance coated on the surface ofsaid particles, said resinous substance the fine particles selected fromthe group consisting of glass beads, zinc oxide, titanium oxide andsilica.

4. A liquid developer according to claim 1, wherein the ratio ofresinous substance to particles of colored substance is from I 30 partsby weight of the former to 1 part by weight of the latter.

5. A liquid developer according to claim 1, wherein the ratio of tonerto fine particles dispersed in the carrier liquid with said toner is0.1:1 to 1:1.

1. A LIQUID DEVELOPMENT FOR USE IN ELECTROPHOTOGRAPHIC TRANSFER PROCESSWHICH COMPRISES: A CARRIER LIQUID HAVING AN ELECTRIC RESISTANCE OF ATLEAST 109*.CM AND A DIELECTRIC CONSTANT UP TO 3 A TONER DISPERSED INSAID CARRIER LIQUID SAID TONER COMPRISING PARTICLES OF A COLOREDSUBSTANCES AND AT LEAST NE RESINOUS SUBSTANCES COATED ON THE SURFACE OFSAID PARTICLES, SAID RESINOUS SUBSTANCE BEING CAPABLE OF PENETRATIONGINTO A PAPER OR A CLOTH TOGETHER WITH FINE INORGANIC PARTICLES BEINGHARDER THAN THE TONER PATRICLES AND HAVING AVERAGE PARTICLE DIAMETERRANGING FROM 1 TO 15Y.
 2. A liquid developer according to claim 1,wherein said resinous substance is selected from the following group ofbutyl rubbers, isobutyl rubbers, chlorinated isobutylene rubbers,modified alkyd resins, isobutylene - butylene copolymers and styrene -butadiene copolymers.
 3. A liquid developer according to claim 1,wherein the fine particles selected from the group consisting of glassbeads, zinc oxide, titanium oxide and silica.
 4. A liquid developeraccording to claim 1, wherein the ratio of resinous substance toparticles of colored substance is from 1 -30 parts by weight of theformer to 1 part by weight of the latter.
 5. A liquid developeraccording to claim 1, wherein the ratio of toner to fine particlesdispersed in the carrier liquid with said toner is 0.1:1 to 1:1.